"Twisted Light" and SETI?

[stargene]

Hi ...

There has been a spate of reports on so-called "twisted
light" recently. A typical one is on the New Scientist
site at

http://www.newscientist.com/article/dn16591-twisted-radio-beams-could-untangle-the-airwaves.html

The following quote from one of the researchers seems to
beg a question, at least for me:

Leyser says that "the information encoded in the twist is
independent of the amplitude and frequency of the radio
waves" - the features of a radio wave more normally used
to encode data. "It is a feature of radio waves that has
not been utilised before."

Is this a game changer in the ongoing SETI program? Ie:
Does this mean that 'ET' signals could have been coming in
all along but we weren't looking for info in the "orbital
spin" of incoming radio waves?

Or would such subtle signals have registered anyway?

Thanks,
Stargene

[Jos Bergervoet]

On Mar 8, 3:04 am, stargene <starg...@sbcglobal.net> wrote:
> Hi ...
>
> There has been a spate of reports on so-called "twisted
> light" recently. A typical one is on the New Scientist
> site at
>

> http://www.newscientist.com/article/dn16591-twisted-radio-beams-could...

This is "old wine in new skins". See Foschini & Gans, "On
limits of wireless communications in a fading environment
when using multiple antennas", 1998. Free download at:
http://course.ie.cuhk.edu.hk/~ieg5230/material/foschini98limit.pdf

What happens now is that people re-invent this by calling
the beam-pattern "orbital angular momentum" or "twisted
light". But this is just another name. Jacksons "Classical
Electrodynamics" has a whole chapter showing how any
radiation pattern can be decomposed in spherical
harmonics with angular momentum index.

The subspace of obtainable radiation patterns with a finite
array of antennas gives a limit of channel capacity, as
analyzed by Foschini. Nothing changes if the basis
vectors in your calculation are the vector spherical
harmonics. In fact the general derivation is much more
elegant and basis-independent.

> Leyser says that "the information encoded in the twist is
> independent of the amplitude and frequency of the radio
> waves" - the features of a radio wave more normally used
> to encode data. "It is a feature of radio waves that has
> not been utilised before."

And that is a lie. The general concept using frequency,
amplitude, polarization, and arrays of antennas was
already know (and its limits as well, see above!)

> Is this a game changer in the ongoing SETI program? Ie:
> Does this mean that 'ET' signals could have been coming in
> all along but we weren't looking for info in the "orbital
> spin" of incoming radio waves?
>
> Or would such subtle signals have registered anyway?

The signals would still be detectable. The techniques are
still based on transmitting RF power to send information.

--
Jos